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When he’s not crowd-surfing on a giant inflatable animal, Andrew McMahon is raising a million dollars for young adult cancer patients and survivors.

Andrew McMahon of Andrew McMahon In The Wilderness greets the audience while performing at the American Express Stage during weekend two of the Austin City Limits Music Festival at Zilker Park in Austin, Texas, on Friday, Oct. 13, 2017. TINA PHAN / FOR AMERICAN-STATESMAN

He started his charity project, the Dear Jack Foundation, after being diagnosed with — and surviving — leukemia in his early 20s, and in the State Farm “Here To Help” lounge at Austin City Limits Music Festival on Friday, he explained why: he saw a “chasm” in services for young adults who had survived or were battling cancer, and he knew from experience that there weren’t enough resources.

He’s also been working with the Love Hope Strength Foundation, a group that works to expand the bone marrow registry for cancer patients.

During the private evening performance, McMahon and bandmate Zac Clark played a stripped-down show consisting of just three songs (that he hadn’t played in his set on the Honda stage earlier in the day) before talking about the importance of giving back to their community.

“That was one of the hottest sets I’ve been onstage to play — I think I just woke up from the blackout,” McMahon said before playing “High Dive,” then laughing his way through an explanation of some of the lyrics in an early Jack’s Mannequin hit, “The Mixed Tape.”

“It was one of the few songs [my wife] took serious issue with — well, not serious issue, but mild — there’s a line in the song that says she broke into my house,” he said, referring to his then-ex-girlfriend, now-wife. “And she’s like, ‘I did not break into your house, I had a key.’ …she did have a key, but at the time she was not invited.”

Before playing “Fire Escape,” he pointed to his wife’s cousins in the back of the room and held a finger up to his lips, then told a story about hazy nights in New York City that inspired his final song.

“It could have been one night, it might have been three,” McMahon said, laughing. “I went to New York City on an off day. I ran into all sorts of weird and wonderful people…I ended up in a basement with all these probably Russian mobsters.”

The song, he said, was about how “you can have these miraculous adventures but it’s where you come home and who you come home to that make all these sidebars worth it.”

For McMahon, home is in California. As somebody who moved around a lot in his youth, his current home in South Orange County, where he’s lived for six years, is the longest he’s lived anywhere.

“The gossip is funny,” he said, laughing. “But when you have a strong community around you … it’s what keeps you grounded, which is something I need a lot of.”

For McMahon, home is also often on the road, so much so that it’s influenced his songwriting in a big way over the years. He referenced his Something Corporate song “I Woke Up in a Car” as an example of a pivotal moment when those experiences changed his songwriting process.

“Up to that point, songwriting wasn’t so story-based. It was the tumult of being an angsty teen and writing about your feelings. But I came home from a Something Corporate tour and had a book of stories about finding yourself on the road with your friends,” McMahon said, noting that his music has changed over the years. “[But] the things that turn me on about songwriting have always been the same — find something you connect to more deeply inside yourself that you’re resolving, that you can’t just say … that’s always been the goal.”

Also in the audience was Katie, McMahon’s sister who famously saved his life when she was a perfect bone marrow match during his cancer treatment. He used his story to encourage others to volunteer in their communities and find what matters to them.

“I was affected by something so profoundly that it made me want to figure out how to participate,” McMahon said. “It’s a crazy thing but to give things away is so much more of a gift to yourself.”